Effect of Supplementation with Synbotic Ice Cream on the immune response, health in general and parameters related to the gut-brain axis in military submitted to field training

Strenuous physical activity, sleep deprivation, and psychological stress are common features of military field training. These extreme conditions often lead to impaired immune function, gastrointestinal disorders and respiratory diseases. Probiotics have been indicated as health promoters due to their direct action on the digestive tract and indirect action on the microbiota-gut-brain axis and respiratory tract. This study aimed to evaluate the effects of supplementation with a synbiotic ice cream on salivary IgA, respiratory and gastrointestinal symptoms, well-being indicators and gut microbiota in young military participants undergoing field training. Eighty military volunteers were recruited and 65 completed the study: one group was supplemented with synbiotic ice cream containing B. animalis, L. acidophilus and inulin, and the other with a placebo ice cream for 30 days. Volunteers were evaluated at baseline, after supplementation and after a 5-day military field training. Saliva was collected for IgA analysis, feces for microbiota sequencing and metabolites analysis, and questionnaires were applied to evaluate health parameters. The study was approved by the Research Ethics Committee of UNICAMP (CAAE: 90850718.8.0000.5404) and enrolled in the Brazilian Clinical Trials Registry (ReBec) (ID: RBR-6DV55J). Salivary IgA decreased after training similarly for both groups (p<0.05; within-group comparisons). The diversity of respiratory symptoms decreased after supplementation and training in the synbiotic-treated group only. We observed a significant decrease in tenseness after supplementation and training in the treated group when compared to the placebo group (respectively, p<0.05 and p<0.001; within-group comparisons). Moreover, the treated group only showed decreased sadness and sleepiness, and increased ease of concentration and energy after supplementation (p<0.05; within-group comparisons) in addition to improved sleep quality after training. Both Bifidobacterium and Lactobacillus genera showed a higher differential abundance after the supplementation period and after military training. Butyric acid presented significant increase only for the synbiotic-treated group post-supplementation period. In conclusion, synbiotic ice cream supplementation for 30 days induced modulation of the microbiota, decreased the number of symptoms related to respiratory tract infection and gastrointestinal symptoms, promoted microbiota-brain-gut axis effects with reduced tension and improved sleep quality of the military group.